I know that these traps are extremely annoying and very against to smooth and fair gameplay (streamers suffer a lot due to this while hunting and using an UE that hits 5 noobchars that had just logged on a High Level hunting ground), but your solution would have some holes too. What if trap players manage to get "Makers" that are on your level range proposed, but they are all on 5-10 hitpoints instantly after logging in? Black/Red skull would be once again here.
I myself got a red skull trap on 2009 or 2010 and I was devasted... The old pvp on Tibia had this flaw that was always exploited (actually it was even worse back in these days). I can't think on anything that would solve 100% the question... At least the Open - PvP servers are harder nowadays to get this trap, unless you mess up with your PvP combat settings.